U.S. Ser. No. 11/405,743 to Himmelmann, filed 17 Apr. 2006, now U.S. Pat. No. 7,385,332, with which this application has common inventorship and ownership, describes various dynamoelectric machines of the permanent magnet type. Such machines may have rotor magnets that are axially displaceable from a corresponding stator assembly to vary rotor-stator magnetic flux interaction, such as to reduce back electromagnetic force (emf) generation in motor operation at high rotational velocities and thereby improve high-velocity motor torque. Rotor displacement may conveniently be by means of hydraulic actuation driven by machine lubrication oil pressure. In such an instance, it may be necessary to have some means of adjusting such lubrication oil pressure to control rotor magnet displacement.